In a typical radio communications network, wireless communications devices, also known as mobile stations and/or user equipments (UEs), communicate via a Radio Access Network (RAN) to one or more Core Networks (CN). The radio access network covers a geographical area which is divided into cell areas, with each cell area being served by a base station, e.g., a radio base station (RBS), which in some networks may also be called, for example, a “NodeB” or “eNodeB”. A cell is a geographical area where radio coverage is provided by the radio base station at a base station site or an antenna site in case the antenna and the radio base station are not collocated. Each cell is identified by an identity within the local radio area, which is broadcast in the cell. Another identity identifying the cell uniquely in the whole mobile network is also broadcasted in the cell. One base station may have one or more cells. A cell may be downlink and/or uplink cell. The base stations communicate over the air interface operating on radio frequencies with the user equipments within range of the base stations.
A Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the second generation (2G) Global System for Mobile Communications (GSM). The UMTS terrestrial radio access network (UTRAN) is essentially a RAN using wideband code division multiple access (WCDMA) and/or High Speed Packet Access (HSPA) for user equipments. In a forum known as the Third Generation Partnership Project (3GPP), telecommunications suppliers propose and agree upon standards for third generation networks and UTRAN specifically, and investigate enhanced data rate and radio capacity. In some versions of the RAN as e.g. in UMTS, several base stations may be connected, e.g., by landlines or microwave, to a controller node, such as a radio network controller (RNC) or a base station controller (BSC), which supervises and coordinates various activities of the plural base stations connected thereto. The RNCs are typically connected to one or more core networks.
Specifications for Evolved Packet System (EPS) have been completed within the 3rd Generation Partnership Project (3GPP) and are further evolved in coming 3GPP releases. The EPS comprises the Evolved Universal Terrestrial Radio Access Network (E-UTRAN), also known as the LTE radio access, and the Evolved Packet Core (EPC), also known as System Architecture Evolution (SAE) core network. E-UTRAN/LTE is a variant of a 3GPP radio access technology wherein radio base station nodes are directly connected to the EPC network, i.e. a radio network controller concept as realized in UMTS with a Radio Network Controller (RNC) does not exist. In general, in EPS the functions of an RNC are distributed between eNBs and the core network. As such, the RAN of an EPS has an essentially “flat” architecture comprising radio base stations without being controlled by RNCs.
A simplified architecture of the LTE system is illustrated as a block diagram in FIG. 1a, including eNBs and evolved packet core nodes. The evolved packet core nodes are illustrated as Mobility Management Entities (MMEs) in FIG. 1a. The eNBs are connected with the MMEs with S1 connections. S1 is an interface between eNBs and MMEs. The MME is used as a control node. For example, the MME is responsible for idle mode UE tracking and paging procedure including retransmissions. The MME is further involved in the bearer activation/deactivation process and is also responsible for choosing a Serving GateWay (SGW) for a UE at the initial attach and at time of intra-LTE handover involving evolved packet core node relocation. The MME is further responsible for authenticating the UE or user of the UE.
In modern cellular networks, the need to provide ever increasing data rates to wireless devices may be met by integrating different Radio Access Technologies (RATs) at the radio level. For example, 3GPP studies in Release-13 better ways to integrate LTE and Wireless Local-Area Networks (WLANs), in particular for operator-deployed WLANs. By integrating LTE and WLAN, throughput provided by individual networks may be aggregated by the wireless devices. For this purpose, 3GPP has recently approved a Release-13 work item [RP-150510, ftp://ftp.3gpp.org/tsg_ran/TSG_RAN/TSGR_67/Docs/RP-150510.zip)] which among others aims at standardizing LTE-WLAN aggregation.
The WLAN technology known as “Wi-Fi” has been standardized by IEEE in the 802.11 series of specifications, i.e., as “IEEE Standard for Information technology—Telecommunications and information exchange between systems. Local and metropolitan area networks—Specific requirements. Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications”.
The IEEE 802.11 specifications regulate the functions and operations of the W-Fi Access Points (APs) and wireless terminals, collectively known as “stations” or “STA,” in the IEEE 802.11, including the physical layer protocols, Medium Access Control (MAC) layer protocols, and other aspects needed to secure compatibility and inter-operability between access points and portable terminals. Wi-Fi is commonly used as wireless extensions to fixed broadband access, e.g., in domestic environments and in so-called hotspots, like airports, train stations and restaurants.
Recently, Wi-Fi has been subject to increased interest from cellular network operators, who are studying the possibility of using Wi-Fi for purposes beyond its conventional role as an extension to fixed broadband access. These operators are responding to the ever-increasing market demands for wireless bandwidth, and are interested in using Wi-Fi technology as an extension of, or alternative to, cellular RATs. Network operators that are currently serving mobile users with, for example, any of the technologies standardized by the 3GPP, including the radio-access technologies known as LTE, UMTS/Wideband Code-Division Multiple Access (WCDMA), and GSM, see Wi-Fi as a wireless technology that may provide good additional support for users in their regular cellular networks.
There is currently quite intense activity in the area of operator-controlled Wi-Fi in several standardisation organisations. In 3GPP, activities to connect Wi-Fi APs to the 3GPP-specified core network are being pursued, and in the Wi-Fi Alliance (WFA), activities related to certification of Wi-Fi products are being undertaken, which to some extent also is driven from the need to make Wi-Fi a viable wireless technology for cellular operators to support high bandwidth offerings in their networks. The term Wi-Fi offload is commonly used and points towards that cellular network operators seek means to offload traffic from their cellular networks to Wi-Fi, e.g. in peak-traffic-hours and in situations when the cellular network for one reason or another needs to be off-loaded, e.g. to provide requested quality of service, maximise bandwidth or simply for coverage.
For a network operator, offering a mix of two technologies that are standardised in isolation from each other, it is a challenge to provide intelligent mechanisms for co-existence.
A WLAN is a network of one or more APs, and may for example be addressed with Service Set Identifiers (SSID)s, Homogeneous Extended Service Set Identifiers (HESSID)s or Basic Service Set Identifiers (BSSID)s.
FIG. 1b, which is a block diagram, illustrates an LTE network and a WLAN network. The networks may be co-located, which means that the WLAN AP and the eNB are implemented in the same node, or non-colocated, meaning that there is an Xw interface between the eNB and the WLAN AP.
LTE-WLAN Aggregation
LTE-WLAN Aggregation (LWA) is a feature wherein a wireless device, such as a UE, may receive and transmit radio signals using wireless communication links to both an eNB and a Wireless Termination (WT). The WT is a logical node operating in the WLAN. The WT may be implemented in an AP, Access Controller (AC), or another physical node. The wireless device may have a separate data bearer configured on the WLAN side. A data bearer may also be split between an LTE and a WLAN connection. When the bearer is split between the LTE and the WLAN connection, i.e. in the split bearer architecture option of LTE and WLAN aggregation, the downlink data is split on the Packet Data Convergence Protocol (PDCP) layer in the eNB. The eNB may route PDCP Packet Data Units (PDUs) dynamically via eNB Radio Link Control (RLC) protocol to the wireless device directly, or via a backhaul channel to a Secondary eNB (SeNB) or via a WLAN Medium Access Control (MAC) protocol to the wireless device.
In the separate bearer architecture, the lower layers of a bearer are switched to LTE or WLAN. Wth lower layers of a bearer is meant layers below the PDCP layer. This means that all PDCP packets of that bearer are routed via either the LTE or the WLAN side. From an eNB perspective, the separate bearer architecture, that has been called 2C in dual connectivity, may be seen as a static routing decision.
FIG. 1c, which is a block diagram, shows a protocol architecture option 3C for LTE-WLAN aggregation which resembles the Release 12 dual connectivity split bearer architecture in LTE, in which the WT assumes the role of the Secondary eNB (SeNB) in LTE. An adaptation layer may be needed in order to adapt PDCP packets to be transported by WLAN. However, depending on implementation the adaptation layer may be at the eNB or WLAN, or parts of it in each node.
In case of an architecture option 2C, there may be either no eNB RLC protocol below the PDCP protocol of the user plane bearer, in case all packets are routed via WLAN to the wireless device; or there may be no WLAN, i.e. all packets may be routed via LTE to the wireless device.
Furthermore, it is assumed that a GTP-U tunnel is established per UE between eNB and WT and that e.g. flow control feedback would come from the WT to the eNB. The LTE-WLAN aggregation function in the WT would receive PDCP PDUs with bearer ID included from the eNB. These PDCP PDUs would be encapsulated into Etherframes and given to WLAN MAC.
From an eNB perspective, the network interface between the LTE and the WLAN networks, e.g. an Xw interface, is always to the WT. However, the wireless device is connected to at most one AP and there may be multiple APs behind one WT. Further, in legacy WLAN the wireless device controls the mobility decisions, while for WLAN/LTE aggregation the eNB controls, to some extent, the mobility between WLAN nodes. WLAN mobility may comprise the procedure of changing which WLAN the UE is connected to and/or served by.
In some scenarios of LTE-WLAN Aggregation the eNB provides the UE with one or more groups of APs, e.g. identified by SSID, HESSID or BSSID, belonging to one or more WLANs. Among these APs WLAN mobility mechanisms apply and LTE-WLAN aggregation is supported. I.e., the UE may perform mobility among these APs transparent to the eNB. That is the UE is allowed to connect to any of the APs within one or more groups of APs, or groups of WLANs, that are allowed for mobility. A mobility set is a set of WLANs that comprise the WLANs that the eNB has indicated to the UE and which the UE may or is allowed to perform mobility between.
However, the eNB does not necessarily know which AP the UE is connected to. This means that it is “transparent” to the eNB which AP and which WLAN the UE is connected to.
UE mobility from the one or more groups of APs, provided by the eNB, and among which WLAN mobility mechanisms apply, to other groups of APs is controlled by the eNB e.g. based on measurement reports provided by the UE.
In other words, the eNB may control the mobility between WLAN nodes by configuring the UE with one or more WLAN identifiers, e.g. SSIDs, HESSIDs and BSSIDs. For example, the eNB may add and/or remove WLANs from the UE's mobility set, for example based on WLAN measurements provided by the UE.
For example, the UE may report to the eNB when the measurements associated with a WLAN indicate that e.g. the signal from the WLAN is good enough for using the WLAN, i.e. when the measurements fulfil some performance criteria. E.g. a performance criterion may be fulfilled when a measure of the measurement is above or below a threshold. Then that WLAN may be added to the mobility set by the eNB. Likewise, the UE may report to the eNB when the measurements associated with a WLAN indicate that the signal from the WLAN is too poor to be used. Then that WLAN may be removed from the mobility set by the eNB. It should be noted that the eNB may also apply other criteria when deciding when to add/remove WLANs from the UE's mobility set.
The eNB may configure the UE regarding when the UE shall send WLAN measurements to the eNB. One example is that the eNB configures the UE to send a WLAN measurement report based on measurement events.
Document 3GPP TS 36.331 version 12.9.0 describes the 3GPP LTE Rel-12 RRC specification that defines measurements prior to LWA being introduced. Measurements are described in section 5.5 of the above document.